5,069 research outputs found
Measuring the Deviation from the Linear and Deterministic Bias through Cosmic Gravitational Lensing Effects
Since gravitational lensing effects directly probe inhomogeneities of dark
matter, lensing-galaxy cross-correlations can provide us important information
on the relation between dark matter and galaxy distributions, i.e., the bias.
In this paper, we propose a method to measure the stochasticity/nonlinearity of
the galaxy bias through correlation studies of the cosmic shear and galaxy
number fluctuations. Specifically, we employ the aperture mass statistics
to describe the cosmic shear. We divide the foreground galaxy redshift
into several bins, where is the redshift of the source
galaxies, and calculate the quantity for
each redshift bin. Then the ratio of the summation of over the bins to gives a measure of the
nonlinear/stochastic bias. Here is the projected surface number
density fluctuation of foreground galaxies at redshift , and is
the aperture mass from the cosmic-shear analysis. We estimate that for a
moderately deep weak-lensing survey with , source galaxy surface number
density and a survey area of , the effective -parameter that represents the deviation from the
linear and deterministic bias is detectable in the angular range of 1'-10' if
|r-1|\gsim 10%. For shallow, wide surveys such as the Sloan Digital Sky
Survey with , , and a survey area
of , a 10% detection of is possible over the angular
range .Comment: ApJ in pres
Effect of Photometric Redshift Uncertainties on Weak Lensing Tomography
We perform a systematic analysis of the effects of photometric redshift
uncertainties on weak lensing tomography. We describe the photo-z distribution
with a bias and Gaussian scatter that are allowed to vary arbitrarily between
intervals of dz = 0.1 in redshift.While the mere presence of bias and scatter
does not substantially degrade dark energy information, uncertainties in both
parameters do. For a fiducial next-generation survey each would need to be
known to better than about 0.003-0.01 in redshift for each interval in order to
lead to less than a factor of 1.5 increase in the dark energy parameter errors.
The more stringent requirement corresponds to a larger dark energy parameter
space, when redshift variation in the equation of state of dark energy is
allowed.Of order 10^4-10^5 galaxies with spectroscopic redshifts fairly sampled
from the source galaxy distribution will be needed to achieve this level of
calibration. If the sample is composed of multiple galaxy types, a fair sample
would be required for each. These requirements increase in stringency for more
ambitious surveys; we quantify such scalings with a convenient fitting formula.
No single aspect of a photometrically binned selection of galaxies such as
their mean or median suffices, indicating that dark energy parameter
determinations are sensitive to the shape and nature of outliers in the photo-z
redshift distribution.Comment: 10 pages, 12 figures, accepted by Ap
Tunable coaxial resonators based on silicon optical fibers
Thermal tuning of a coaxial fiber resonator with a silica cladding surrounding an inner silicon core is investigated. By pumping the silicon with below bandgap light, it is possible to redshift the WGM resonances
The Evolution of Radio Galaxies at Intermediate Redshift
We describe a new estimate of the radio galaxy 1.4 GHz luminosity function
and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and
color selection have been used to select Bj<23.5 early-type galaxies from the
Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields.
Approximately 230 radio galaxies have then been selected by matching early-type
galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz
luminosity function of radio galaxies measure significant evolution over the
observed redshift range. For an Omega_M=1 cosmology the evolution of the radio
power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and
3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray
selected AGN and is consistent with the same physical process being responsible
for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A
Imprint of Reionization on the Cosmic Microwave Background Bispectrum
We study contributions to the cosmic microwave background (CMB) bispectrum
from non-Gaussianity induced by secondary anisotropies during reionization.
Large-scale structure in the reionized epoch both gravitational lenses CMB
photons and produces Doppler shifts in their temperature from scattering off
electrons in infall. The resulting correlation is potentially observable
through the CMB bispectrum. The second-order Ostriker-Vishniac also couples to
a variety of linear secondary effects to produce a bispectrum. For the
currently favored flat cosmological model with a low matter content and small
optical depth in the reionized epoch \tau \la 0.3, however, these bispectrum
contributions are well below the detection threshold of MAP and at or below
that of Planck, given their cosmic and noise variance limitations. At the upper
end of this range, they can serve as an extra source of noise for measurements
with Planck of either primordial nongaussianity or that induced by the
correlation of gravitational lensing with the integrated Sachs-Wolfe and the
thermal Sunyaev-Zel'dovich effects. We include a discussion of the general
properties of the CMB bispectrum, its configuration dependence for the various
effects, and its computation in the Limber approximation and beyond.Comment: 17 pages, 10 figures (with emulateapj.sty); submitted to Ap
A New Algorithm for Computing Statistics of Weak Lensing by Large-Scale Structure
We describe an efficient algorithm for calculating the statistics of weak
lensing by large-scale structure based on a tiled set of independent
particle-mesh N-body simulations which telescope in resolution along the line
of sight. This efficiency allows us to predict not only the mean properties of
lensing observables such as the power spectrum, skewness and kurtosis of the
convergence, but also their sampling errors for finite fields of view, which
are themselves crucial for assessing the cosmological significance of
observations. We find that the nongaussianity of the distribution substantially
increases the sampling errors for the skewness and kurtosis in the several to
tens of arcminutes regime, whereas those for the power spectrum are only
fractionally increased even out to wavenumbers where shot noise from the
intrinsic ellipticities of the galaxies will likely dominate the errors.Comment: 12 pages, 13 figures; minor changes reflect accepted versio
First cosmic shear results from the Canada-France-Hawaii Telescope Wide Synoptic Legacy Survey
We present the first measurements of the weak gravitational lensing signal
induced by the large scale mass distribution from data obtained as part of the
ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in
this analysis are from the Wide Synoptic Survey, which aims to image ~170
square degree in five filters. We have analysed ~22 deg2 (31 pointings) of i'
data spread over two of the three survey fields. These data are of excellent
quality and the results bode well for the remainder of the survey: we do not
detect a significant `B'-mode, suggesting that residual systematics are
negligible at the current level of accuracy. Assuming a Cold Dark Matter model
and marginalising over the Hubble parameter h=[0.6,0.8], the source redshift
distribution and systematics, we constrain sigma_8, the amplitude of the matter
power spectrum. At a fiducial matter density Omega_m=0.3 we find
sigma_8=0.85+-0.06. This estimate is in excellent agreement with previous
studies. Combination of our results with those from the Deep component of the
CFHTLS enables us to place a constraint on a constant equation of state for the
dark energy, based on cosmic shear data alone. We find that w_0<-0.8 at 68%
confidence.Comment: Submitted to Ap
Ultra-high energy cosmic rays may come from clustered sources
Clustering of cosmic-ray sources affects the flux observed beyond the cutoff
imposed by the cosmic microwave background and may be important in interpreting
the AGASA, Fly's Eye, and HiRes data. The standard deviation, sigma, in the
predicted number, N, of events above 10^{20} eV is sigma/N = 0.9(r_0/10
Mpc)^{0.9}, where r_0 is the unknown scale length of the correlation function
(r_0 = 10 Mpc for field galaxies). Future experiments will allow the
determination of r_0 through the detection of anisotropies in arrival
directions of ~ 10^{20} eV cosmic-rays over angular scales of Theta ~ r_0/30
Mpc.Comment: Accepted for publication in Astrophysical Journa
Universality of power law correlations in gravitational clustering
We present an analysis of different sets of gravitational N-body simulations,
all describing the dynamics of discrete particles with a small initial velocity
dispersion. They encompass very different initial particle configurations,
different numerical algorithms for the computation of the force, with or
without the space expansion of cosmological models. Despite these differences
we find in all cases that the non-linear clustering which results is
essentially the same, with a well-defined simple power-law behaviour in the
two-point correlations in the range from a few times the lower cut-off in the
gravitational force to the scale at which fluctuations are of order one. We
argue, presenting quantitative evidence, that this apparently universal
behaviour can be understood by the domination of the small scale contribution
to the gravitational force, coming initially from nearest neighbor particles.Comment: 7 pages, latex, 3 postscript figures. Revised version to be published
in Europhysics Letters. Contains additional analysis showing more directly
the central role of nearest neighbour interactions in the development of
power-law correlation
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